The present invention relates to a process for shirring tubular casings, in particular sausage casings, in which the casing is conveyed in the direction of its longitudinal axis, folds are formed in a shirring area under the action of a shirring force, and the casing leaves the shirring area as a shirred casing portion. At least the casing portion present in the shirring area and the shirred tubing portion are continuously internally supported so that shirring occurs in the inflated state. When the shirred tubing has reached a predetermined length, the transport of the casing is momentarily interrupted, the internal support is removed from the severing region which follows the shirring region, and the length of shirred casing is severed in the severing region and removed. The severed portion of shirred tubing is called a shirred stick.
The invention also relates to an apparatus for performing the above-described process. Known apparatuses for shirring tubular casings essentially comprise a shirring mandrel which is located in the interior of the casing to be shirred; conveying elements for moving the casing supplied from the free end of the shirring mandrel in the inflated state over the shirring mandrel; a shirring tool which acts on the outer circumference of the tubing and through which the shirring mandrel, supporting the casing from inside, extends; and a severing tool, by which the shirred sticks are cut off after reaching a predetermined length.
If, however, self-supporting shirred sticks are to be produced, which is usually the case, the tubular casing must be very densely shirred. The apparatuses then require an abutment which presents a counterforce to the shirring force and which simultaneously allows for an advance movement of the shirred tubing portion.
U.S. Pat. No. 4,359,806, for example, discloses the use of an abutment in the form of a stop which is arranged on the shirring mandrel in such a way that it can be shifted along the longitudinal axis of the mandrel, so that during the formation of the shirred stick the abutment can perform a controlled backward-directed movement. In this apparatus, the shirring mandrel is comprised of one single piece. In the working position, it must extend through the whole stirring tool, which means that before a shirred stick can be cut off, it has to be completely retracted from the shirring tool, until its end is freely positioned in front of the shirring tool.
In order to cut off and remove a shirred stick from the unshirred tubing portion, it is furthermore necessary, using this apparatus, first to stop the shirring tool before the shirring mandrel can be axially removed therefrom, in the direction of shirring. After cutting off the casing and pivoting away the shirring mandrel carrying the just formed shirred stick, an empty shirring mandrel is inserted into the shirring tool, in a direction opposite to the direction of shirring. Only then can the shirring tool be turned on again. Even though the axial path of travel of the shirring mandrel is relatively short, there are long dead travel times between the individual shirring operations, due to the alternating acceleration and slow-down of the shirring tool.
It is impossible, however, to continue the rotation of the shirring tool while the shirring mandrel is withdrawn. In this state, the tubing material is no longer internally supported and therefore would be squeezed by the strong mechanical stress caused by the shirring tool. It would also be difficult to push the shirring mandrel into the squeezed tubing material.
Yet another disadvantage of this apparatus resides in the fact that an exact centering of the shirring mandrel within the shirred tubing portion is very difficult during the formation of the shirred stick and can only be accomplished by means of rather complicated appliances which moreover impede an easy withdrawal of the shirred stick. Additional technical difficulties may arise because, at the beginning of the shirring process, the profiled rollers intended for centering the shirring mandrel must slide from a counterhold sleeve onto the shirred stick being formed. As a result, the shirring mandrel is horizontally displaced by the profiled rollers due to their circular motion. For this reason, it is not possible to keep the position of the shirring mandrel exact during shirring.
Apparatuses which employ a single, stationary shirring mandrel are also known. With these apparatuses it is difficult, however, to cut the casing neatly.
German Pat. No. 1,295,414 (equivalent to U.S. Pat. No. 3,112,517) discloses an apparatus of this type, wherein severing of the shirred stick from the shirred tubing portion is performed at a distance from the shirring tool and in the direction of shirring, after a stop member intended for exerting a counterforce to the shirring force. Severing is performed by scoring and not by cutting. Over the stripping end of the shirring mandrel, the severed shirred stick is pushed onto an axially extending adjacent receiving mandrel, by means of a special stripping device. The stripping end of the known shirring mandrel is held by clamping jaws which have to be unclamped for stripping off the shirred stick. The receiving mandrels are installed on a turret which rotates stepwise and on which the shirred sticks are compressed and subsequently discharged.
U.S. Pat. No. 3,209,398, discloses an apparatus wherein the shirred stick is pushed onto an axially extending, adjacent transport mandrel by means of a special stripping device and further processed on said transport mandrel.
It is a substantial disadvantage of these known apparatuses that the shirred sticks cannot be cut off neatly, so that the ends of the stick tend to become ragged. Moreover these apparatuses are of rather complicated constructional design. The clamping jaws for the second end of the shirring mandrel according to German Pat. No. 1,295,414 and the stripping devices are difficult to control. Use of these known apparatuses also involves the danger that, in the case of relatively densely shirred sticks, the tubing material is damaged in the process of being pushed from the shirring mandrel onto the transport or receiving mandrel. Yet another disadvantage of these shirring apparatuses resides in the fact that the shirring mandrel cannot rotate about its longitudinal axis or at least a great technical expense would be required to make it rotate. Such a rotary movement would cause the shirred tubing portion to rotate during the shirring process, which would result in particularly densely shirred sticks.
In contrast to the previously mentioned apparatuses, the sausage stuffing machine disclosed in U.S. Pat. No. 4,358,873 comprises a shirring unit wherein the shirring mandrel includes two mandrel members which during the shirring process can be engaged in straight alignment. After completion of a shirred tubing portion, the second mandrel member, seen in the direction of shirring, is axially displaced, and the shirred tubing portion is cut off and pivoted away on the second mandrel member, which is then replaced by an empty mandrel member.
This unit is, however, even less suitable to produce densely shirred, self-supporting sticks which are resistant to bending than are the apparatuses described in the previously mentioned publications. For example, it does not possess any elements by which the folded casing could be further compressed. Moreover the cavity of the shirred tubing obtained exhibits neither a uniform diameter nor a smooth internal wall, because the air supply device for inflating the tubular casing is installed outside the shirring mandrel and extends through the shirring tool.
Furthermore, this unit is not intended to produce very densely shirred sticks. The resulting shirred tubing portions are not to be sold as self-supporting shirred sticks, but are permanently internally supported, and immediately after their preparation they are pushed onto the stuffing horn of a sausage stuffing machine, filled with sausage meat and tied off at predetermined lengths.